1. Field of the Invention
This invention relates to an improvement in a baking and drying furnace for containers such as cans for canned food, which are coated or printed.
2. Description of the Prior Art
Where containers such as cans have been coated or printed for ornamental purposes, after which they are dried and baked, it has been heretofore customary to use a baking and drying furnace or oven known as a "pin oven". Coated and printed cans move while being hung on pins through the furnace under the atmosphere of high temperature. The furnace of this system is suffered from disadvantages in that since the can is heated only from the surface thereof, the heating efficiency is poor and that since the pin is in contact with the inner surface of the can, the furnace cannot be used to dry and bake the coating of the inner surface.
On the other hand, a baking and drying furnace has been recently made practicable, of the type in which a suction hole is disposed partly of an opening of a can which moves while being placed with an opening thereof directed downwardly through the furnace under the atmosphere of high temperature, and after the high temperature atmosphere within the furnace has been once flown into can from the other portion of the opening of the can, it is suctioned from the suction hole. (For example, see Japanese Patent Application Laid-open No. 52-143548)
The furnace of the type as described has various advantages in that since the can is heated from both inner and outer surfaces thereof by the high temperature atmosphere, the heating efficiency is extremely high, and that only the open edge of the can comes to contact with the transporting belt during the drying and baking, and the inner and outer surfaces of the can may be simultaneously coated and simultaneously dried and baked.
However, the can is retained on the transporting belt during the drying and baking only by a pressing force caused by a difference between atmospheric pressure within the furnace and atmospheric pressure within the can which is suctioned to be lowered. Because of this, a trouble in tumbling of cans during transportation occurs owing to curves or vibrations of transporting belts which often comprise metal belts such as stainless, and especially in cans such as beverage cans frequently used recently, the height of the can is greater than the diameter thereof and the centroid position thereof is high whereby the trouble of this kind tends to occur.
On the other hand, if an attempt is made to increase the pressing force by lowering the atmospheric pressure within the can, the suction force of the suction opening is naturally increased, as a consequence of which there poses problems in that the air stream is formed into a turbulent flow to blow down the can, or a coating on the surface of the can is carried away resulting in an uneven coated film, and as the case may be, the coating falls down and droplets thereof are suctioned and adhered to the inner surfaces of the can. Thus, the problems have not been solved merely by increasing the suction force. force.